1. Field of the Invention
The present invention relates to a planographic printing method, an original printing plate and a planographic printing press. In particular, the invention relates to a simplified planographic printing method for making plates without any development, an original printing plate used therefor, and a printing press therefor.
2. Description of the Related Art
Planographic printing has widely been utilized along with presensitized plates (hereinafter called “PS plates”) in the field of printing as a printing process suited to the needs in the printing market where a cost-reduced and simplified printing process is desired. As to the PS plates, a wet plate-making process is employed since a printing plate is prepared by a development process after images are recorded thereonto. Further simplification is desired in the recent printing market. In response to the market needs, as especially simplified plate-making processes not requiring any development in planographic printing, a number of plate-making processes have been proposed, by which printing plates are prepared by forming hydrophilic and hydrophobic image-by-image distributions using photo catalyst substances whose polarity may change by the irradiation of activation light. In these processes, since changes in a polarity, which are enough to separate ink acceptability and ink repulsion property in irradiation areas and non-irradiation areas, can be produced by only performing image-by-image exposure on an original plate, the original plate may be applied to printing without further process. Therefore, it can be said that these printing and plate-making processes are remarkably simple.
For example, in Japanese Unexamined Patent Publication Nos. 11-105234, 11-138970, 11-138971, 11-143055, and 11-174664, a printing and plate-making process has been developed, which hydrophilic and hydrophobic image distributions are formed by changing the polarities by irradiating activation light onto an original printing plate having a thin layer of a photo catalyst is metal compound. Also, in Japanese Unexamined Patent Publication No. 10-250027, such a process has been developed, which can carry out electrostatic printing after forming hydrophilic image areas on the hydrophobic surface having photo catalyst power by irradiating activation light thereonto as per image.
If the polarity conversion by activation light of the photo catalyst substances is utilized, it is very advantageous in view of simplification. However, if the printing quality and printing resistance are improved in addition thereto the practical value thereof can be further increased as a printing plate. Therefore, improvements will be attempted in terms of these points. Accordingly, it is necessary to severely distinguish the irradiation areas from non-irradiation areas for further improvement.
In Japanese Unexamined Patent Publication No. 10-25131, such a process has been proposed as a means for strengthening the distinction between them, which the difference between the hydrophilic property and hydrophobic property is strengthened by using silica or alumina materials on the surface in terms of strengthening the hydrophilic property and using a fluorine-based gas hydrophobic agent to improve the hydrophobic property. In addition, in Japanese Unexamined Patent Publication No. 11-133631, such a process has been disclosed, which improves the distinction-between the hydrophilic property and hydrophobic property by decomposing the hydrophobic substances in the irradiation areas by the irradiation of activation light where a hydrophobic substance layer is provided on an original plate having photo catalyst power.
However, it is desirable that the distinction property of the irradiation areas and non-irradiation areas is further improved in original printing plates in which the polarity conversion of the photo catalyst substances is utilized. It is also desirable that a substantial shortcoming of the polarity changing rate in line with the irradiation of activation light being slow is corrected. If the polarity changing rate is slow, the sensitivity is lowered, wherein another problem occurs, that is, the depicting time by activation light is increased, and energy consumption is accordingly increased.